Daytime off solar cell flasher circuit



Aug. 25, 1959 Filed June 6, 1958 J. J. COLEMAN 2,901,669

DAYTIME OFF SOLAR CELL FLASHER CIRCUIT 2 Sheets-Sheet 1 IlJ @may@av/)603% {5mi/MWL;

Aug. 25, 1959 .1. J. COLEMAN 2,901,669

DAYTIME OFF SOLAR `CELL FLASHER CIRCUIT C Filed June 6, 1958 2Sheets-Sheet 2 United States Patent y 2,901,669 DAYTiME orr SOLAR CELLFLASHER CIRCUIT Joseph J. Coleman, Freeport, Ill., assignor, by mesneassignments, to Servel, Inc., Evansville, Ind., a corporation ofDelaware This invention relates to asher signals and more specificallyrefers to a unit operated by transistors and one which is automaticallydisabled during the daylight period.

Flasher warning signals have become widely used for many purposes. Theyare used to warn motorists and pedestrians at night in road repair andexcavation areas, and lare also used to warn motorists of obstaclespresent on the highways. These units generally comprise a lamp whosecircuit is intermittently switched on and olf by meanspoi:` amechanically controlled asher unit. More recently switching circuitsutilizing transistors have been proposed for this purpose. However, allunits of this type must be manually turned off during daylight hours ifthe batteries are to be conserved. This requires the eX- penditure ofmany man-hours of labor where a large installation of such warningdevices is used, especially if the devices are placed at distancesremote from one another.

It is an object of this invention to provide an apparatus which may beusedto generate flashing warning signals, which is fool-proof and willoperate over long periods of time without attention.

It is a further object to provide such a flasher unit which will beautomatically disabled during daylight hours to conserve electricalenergy of its batteries, and automatical* 1y reactivated with theapproach of darkness.

Other objects and advantages of the present invention will be apparentfrom an examination of the following description and drawings in which:

Fig. l is a schematic diagram of a transistor-operated flasher unitdisclosed in the art;

` Fig. 2 is a schematic diagram of a transistor-operated asher unit ofthe present invention utilizing solar cells to prevent its operationduring daylight hours; and

Figs. 3-7 are schematic diagrams of alternative forms of the invention.

According to the present invention it has been found that ifphotoelectric devices, especially solar cells, in sufiicient number andin the proper arrangement are placed in the control circuit of at leastone of the transistors of a transistor-operated ilasher in such anarrangement that when light strikes the cells, they will so bias thetransistors in the circuit to stop the conduction of the currentthereby, normal operation of the flasher unit will not be interferedwith during darkness, but during daylight hours the unit willautomatically remain out of operation. The operation of the inventionwill be more fully explained in the following description.

Referring to Fig. 1, a battery (not shown) supplies current in thisknown circuit at terminals I1 and 2. A lamp 3 and a P-N-P junctiontransistor 4 are placed in series in a grounded collector circuit. Thebase of the transistor 4 is normally biased to prevent a flow of currentfrom the emitter through the base to the collector. This results in onlya very minute current flow in the lamp-cir cuit. During the period whenthere is substantially no ilow through the transistor 4, a small currentows through the lamp 3 and resistor 4 to charge the condenser 5 which ineifect is connected between the positive and negative terminals withresistor 14 and lamp 3 in series therewith. Resistors 6 and 7 togetherconstitute a potentiometer. The potentiometer -timid-terminal a isconnected to the base of an N-P-N junction transistor 8 and provides thebiasing current for the transistor.. When voltage. is first appliedacross the terminals t1 and 2, the transistor 4 is so biased that itwill allow substantially no current to ow through the emitter-collectorcircuit, and as a result the bulb 3 does not light. As the condenser '5becomes charged, the potential difference across itsterminals increases,also increasing the potential diierence across the resistances 6 and 7.Part of the current passing through the bulb 3 goes through resistor 14to charge condenser 5, and a part goes through resistances 6 and 7 toterminal 2. Before the condenser'is charged, the potential atmid-terminal ais not great enough to trigger the transistor 8. However,when the condenser reaches the state where it is substantially fullycharged, the potential at a rises to a value suiicientvtorl trigger thetransistor. This causes the condenser 5 to discharge through theemitter-collector circuit of the N-P-N transistor 8, through resistor 9,through the base-emitter circuit of the P-N-P transistor 4 to thepositive terminal 2. `This discharge current through the base-emittercircuit of the P-N-P transistor triggers it by biasing it in a forwarddirection to allow the current to flow therethrough to light up thebulb. The bulb will be lit during the interval of condenser discharge.Thereafter, the bias applied to the P-N-P transistor once moresubstantially cuts oif the current through the lamp, causing it tobecome extinguished. With the lamp current olf, the condenser S can oncemore begin to charge. Y

This sequence will be continually repeated to cause intermittent flashesof light. The ratev of charge of the condenser 5 is controlled by thevalue of the resistor 14 together with the resistance of the lamp 3. Therate of discharge of the condenser is determined by the value of theresistor 9. Consequently, the interval during which the` lamp remains onand olf during the blinking cycle as well as the frequency of the cyclemay be determined by the choice of the values of these resistors,together with the value of the condenser 5.

Referring to Fig. 2, a circuit similar'in arrangement and operation tothat of Fig. 1 is shown except that solar cells 10 have been insertedbetween the potentiometer midterminal a and the base of the transistor8. The solar cells are so arranged that when no light shines upon theiractivating surfaces, the current is free to flow from the terminala tothe transistor base, but that when light shines on their surfaces, thecurrent supplied by the solar cells opposes the biasing current suppliedby the terminal a. Thus, during darkness the asher circuit works in thesame manner as the circuit shown in Fig. 1. However, during daylighthours when light falls upon the solar cells, the

transistor 8 is so biased by the current produced in the solar cellsthat it cannot be triggered to discharge the condenser 5. As a resultthe condenser 5 will remain 'in biases the N-P-N transistor so that thecondenser 5 canl not discharge therethrough, and the ycondenser remainscharged until the disabling voltage applied by the solar cell isremoved, at which time the asher circuit resumes normal operation. ,y

Fig. 4 shows another circuit arrangement using the solar cell control.Here the disabling function is accomplished by having the currentresulting from light energy 'p falling on the solar cell flow in such adirection asto'prevent the condenser 5 from becoming charged. The emit-Patented yAug. v25, 1959 g 3 ter of the N-P-N'transistor 8 becomespositive with the result that the transistor Ydoes not conduct current.Consequently, as long as the solar cell is activated, the P-N-Ptransistor 4 isso biased by lthe N-P-N transistor y8 that thelamp doesnot'flight.

Fig. 5 vshows still Yanother circuit "arrangement which is quitesensitive yand which may be operated with the use of only a single solarcell "10. vThe solar cell'when illuminated produces abias'current acrossthe base and emitter of the P-N-'P transistor 4. As'a result, 'thetransistor is never in the conducting condition as long as the solarcell is activated.

Fig. 6 illustrates 1a circuit simi-lar to that of Fig. 2, but in whichthe transistors are interchanged. P-N-P transistor 8a `is controlled bysolar cells 1t) and triggered by condenser `5, while N-P-N'rtransistor4a controls the lamp circuit. The resulting operation, however, issimilar to that of the circuit in Fig. 2.

Fig. 7 illustrates Aa circuit wherein the solar cell has been replacedby a photo-resistive device such as a photodiode, an example being 'the1N77 Germanian diode. When light falls on the sensitive portion of thephotoresistive device 1(a, the resistance decreases so that thecondenser 5 canot become charged. In darkness, the resistance of thediode becomes high, allowing the condenser to become charged, and thenormal function of the flasher circuit to be resumed.

The term solar cell yas used in the specification and claims refers tothe photronic or photovoltaic type, i.e. cells which generate a largeamount of electrical current when they are subjected to light radiation,as opposed to phortocells which establish electrical potential butproduce very little current. Among the suitable types of solar cells isthe B-2M self-generating selenium cell sun battery. Although otherphotoelectric devices described in relation to this invention may beused, greatly superior results may be obtained with solar cells sincethey halve the ability to supply the rather large currents needed tocontrol transistors. Itis possible to use photoconductifve cells such asthe ClaireXCL-Z or CL-3 which are of the cadmium sulde or cadmiumselenide types, but the results obtained will be considerably inferiorto those obtained with solar cells.

The number of solar cells required in a particular oircuit of thepresent invention varies with the application and with `the type oflcircuit used. In the circuit of Fig. 2, several solar cells in seriesyare indicated. On the other hand, the circuits lof Figs. 3, 4 and 5 aresomewhat more sensitive and the use off only 'one solar cell issatisfactory. Where the hashing fdevices are to be used under poorillumination, it may be -necessary to increase the number of solar cellsused.

Among the suitable semi-conductive devices which may be used aretransistors of the point contact, surface barrier, or junction type. Thejunction transistor is preferred. In order that the circuits functionproperly, the transistors should be oppositely conducting with respectto each other, For example, if the transistor acting as a switch for thelamp current is a P-N-P type, the triggering transistor should be anN-P-N type. On the other hand, if vthe switching transistor is an N-P-Ntype, the triggering transistor should be a P-N-P type. The preferredarrangement is to have a P-N-P junction transistor as the switchingtransistor and an N-P-N junction transistor as the triggeringtransistor.

Although they are not to `be considered as limiting in any way,following are listed suitable values which may be used for vthe variouscomponents inthe vcircuits shown in the gures.

Condenser 5 mfd 50 The lamp may be one designed to operate at 5 volts at:09 amps. The P-N-'P "transistors 4 and 8a' may be any one, for example,of types 2N188A, 2Nl86, 2N189, or 2N319. The N-P-N transistor may be anyone, for example, of types ID2A10, 2N169A, or 2N35. In some cases it maybe necessary to Vchange the values of the resistors .somewhat inaccordance with the known characteristics of the transistors, to provideproper biasing and electrode currents.

The flasher devices of the present invention havemany advantages.Because they utilize transistors, they will operate almost indefinitelywithout attention or need for part replacement. 'The incorporation of anautomatic turn-off during daylight hours accomplishes a large saving inoperating costs, since the only current drain during daylight hourscomprises the extremely small leakage through the condenser andextremely small current across the transistor junction. Because of theautomatic-turnorf feature, the 'need for a crew of men in Ia multipleinstallation to turn the 'ashers on eac'h night and toturn them olfYeach morning is obviated. Additionally, the tlasher deviceswill'operateover long periods of time without the need for lbatterychange since the current drain is so exceptionally W.

I claim:

l. In an electric lamp asher comprising a lpair of terminals adapted tobe connected vto a direct current source, an electric lamp in seriescircuit therewith, a pair of semiconductive devices each of which is ofan oppositely conducting type with respect to the other, each of saiddevices having a control element and a pair of load elements, the loadelements ofthe first of said semiconductive devices being in series withsaid lamp circuit, and the control element of said rst semiconductivedevice being connected to a load element of said second semiconductivedevice, 'and means for intermittently applying a current to the controlelement of said second semiconductive device, the improvement whichcomprises means for disabling said flasher during daylight, said meanscomprising a solar cell connected to said second semiconductive device`to biasl it to the conducting con-V dition When less `than apredetermined amount of light falls on said photoelectric device and tothe nonconducting condition when more than said predetermined amount oflight falls'on said photoelectric device.

2, An electric lamp flasher according to claim l wherein saidsemi-conductive devices are junction transistors.

3. An electric lamp asher according to claim 2 wherein said means forintermittently applying a current to the control element of said secondsemiconductive device is a capacitance-resistance network connected Vtosaid direct current source.

4. In an electric lamp flasher comprising a pair of terminals adapted tobe connected to a direct current source, an electric lamp in seriescircuit therewith, a pair of transistors each of which is of anoppositely conducting type with respect to the other, each of saidtransis tors having a base, an emitter, and a collector, the emitter andcollector of the rst of said transistors being in series with said lampcircuit and the base of said transistor being connected to collector ofsaid second transistor, and means for intermittently applying a currentto the base and collector of said second transistor, the improvementwhich comprises means for disabling said asher during daylight, saidmeans comprising a solar cell connected to said second transistor tobias it to the conducting condition when less than a predeterminedamount of lights falls on said photoelectric device and to thenonconducting condition when more than said predetermined amount oflight falls on said photoelectric device.

5. An Velectric lamp flasher according to claim 4 wherein said rsttransistor is of the P-N-P type and said second transistor is of theN-P-N type.

6. An electric lamp asher according to claim 4 5 wherein said firsttransistor is of the N-P-N type and said second transistor is of theP-N-P type.

7. In an electric lamp flasher comprising a pair of terminals adapted tobe connected to a direct current source, an electric lamp in seriescircuit therewith, a pair of junction transistors one being of the P-N-Ptype and the other of the N-P-N type, each of said transistors having abase, an emitter and a collector, the emitter and collector of the P-N-Ptransistor being in series with said lamp circuit, and the base of theP-N-P transistor being connected to the collector of the N-P-Ntransistor, a condenser connected to be charged by said direct currentsource, one of the terminals of said condenser being connected to theemitter of the N-P-N transistor, the other terminal of said condenserbeing connected to the emitter of the P-N-P transistor, a pair ofresistors in series forming a Voltage divider connected across theterminal of said capacitor, the junction between said series-connectedresistors being connected to the base of said N-P-N transistor, theimprovement which comprises means for disabling said flasher duringdaylight, said means comprising one or more solar cells connected inseries between the base of said second transistor and the junctionbetween said series-connected resistors, said solar cells biasing saidN-P-N transistor to the nonconducting condition when more than apredetermined amount of light is falling on said solar cells, andallowing said N-P-N transistor to become biased to the conductingcondition when less than said predetermined amount of light falls onsaid solar cells.

References Cited in the file of this patent UNITED STATES PATENTS2,773,219 Aron Dec. 4, 1956 2,788,449 Bright Apr. 9, 1957 2,825,003Hanson Feb. 25, 1958 2,829,257 Root Apr. 1, 1958 2,833,938 Pinckaers May6, 1958 2,840,727 Guggi June 24, 1958

